Survivable ground antenna system

ABSTRACT

A survivable ground antenna system which relies upon its location within the earth for protection from natural or man-made forces. The antenna system utilizes a &#39;&#39;&#39;&#39;point source&#39;&#39;&#39;&#39; feed located within a main reflector in conjunction with a subreflector for communicating with a target. The feed is adjustably mounted therein and capable of operation even though located beneath the surface of the ground.

United States Patent [191 McGraw SURVIVABLE GROUND ANTENNA SYSTEM [76] Inventor: Thomas F. McGraw, 7538 Axton St., Springfield, Va. 22151 [22] Filed: Dec. 13, 1972 [21] Appl. N0.: 314,624

[52] U.S. Cl 343/719, 343/781, 343/841, 343/912 [51] Int. Cl. H0lq 1/04 [58] Field of Search... 343/719, 781, 840, 841, 912, 343/915 [56] References Cited UNITED STATES PATENTS Suliteann 343/872 1451 Feb. 5, 1974 Primary Examiner-Eli Lieberman Attorney, Agent, or Firml-1arry A. Herbert, Jr.

[ ABSTRACT A survivable ground antenna system which relies upon its location within the earth for protection from natural or man-made forces. The antenna system utilizes a point source feed located within a main reflector in conjunction with a subreflector for communicating with a target. The feed is adjustably mounted therein and capable of operation even though located beneath the surface of the ground.

10 Claims, 3 Drawing Figures BACKGROUND OF THE INVENTION This invention relates generally to antenna systems and, more particularly, to an antenna system with a high degree of survivability for use with communications satellites.

Communications satellites are usually placed in orbit about the earth to serve as a radio relay in long range communications systems. Its primary function is to intercept radio signals from the ground and either retransmit or redirect these signals back to receiving stations. Use of satellites is thus analogous to that of the ionosphere in high-frequency systems. Satellites are capable, however, of much greater information capacity, offer relative freedom from ionospheric variation, and permit greater flexibility in system design and application.

Historically, the antenna systems used to communicate with these satellites are of massive construction made up of vulnerable dish reflectors. They may be 60 feet in diameter and may stand more than 100 feet off their foundations. Furthermore, they are often lightly sheltered from weather environment by a selfsupporting dome structure. These large antennas are affected by mechanical distortion due to winds, temperature, and ice and require extensive design consid erations and expense to overcome these problems. They are also susceptible to blasts and wide-angle stray electromagnetic radiation.

The effects of such mechanical or electronic distortion on the reflectors translate directly into frequency limitations and reduced efficiency for the antennas as well as for the whole communications system. Usually the structural massiveness and the protective domes offer at least partial relief; however, these are expensive and still somewhat vulnerable. The large moving reflectors also require complex steering mechanisms and inertia-cancelling devices, while the domes require substantial maintenance in many climates. These considerations contribute to the very high cost of ground antennas.

Many cost estimates for large steerable parabolodial antennas have been made and the following analysis is presented to show that an alternative design is a necessary expedient.

The weight of the structure is approximately proportional to: V' R (f Considering that foundation size and cost is proportional to the support structure weight, estimates of the cost relation are cost=1 V -"R o-' cost per unit area of the paraboloid is given as:

Where V is the maximum operational wind speed, is the maximum permissible deflection, and D is the di' ameter. R is the length of the radial support. Because of the variation of material properties, selection of aluminum over steel, for example, does not effectively alter the basic cost considerations. There is not much information available on costing for large spherical antennas, but, in the case of the steerable paraboloids, the significant relationship with winds, deflections, and diameter, can easily be seen.

It is therefore clearly evident that an antenna must be constructed which is not dependent on the expensive characteristics of the past.

SUMMARY OF THE INVENTION The instant invention sets forth a survivable ground antenna system which overcomes the problems set forth hereinabove.

THe antenna system of this invention is one which is practically invulnerable because it can be utilized while positioned flush with the ground surface. The basic design of the instant invention is made up of a hemispheric reflector of a solid metallic surface mounted in a rigid concrete supporting cup within a hollowed portion of the ground. The antenna is capped by a light, slightly domed rf-transparent disk which serves solely as a Weather cover. The point-source feed is mounted through an aperture within the supporting cup and is roughly on a line which includes the target and the center of generation of the sphere. The pointsource feed is directed toward the target, and is reflected to or from the spherical reflector via a gregorian subreflector. This assembly is further positioned as a unit by hydraulic cylinders for fine aiming.

The entire antenna system is mounted flush with the surface of the earth which greatly reduces blast damage from hostile or natural events. All electronic components except the point-source are isolated behind the metal reflector and below the ground. This represents a major resistance to the effects of electromagnetic pulse, which induces damaging currents into exposed electronic equipmnt as an effect of nuclear detonation. Furthermore, the construction of the instant invention produces a significant savings over steerable parabolas of an equivalent surface.

It is therefore an object of this invention to provide a survivable ground antenna system which can resist most natural and hostile environmental conditions.

It is a further object of this invention to provide a survivable ground antenna system which due to its location within the earth and its inherent narrow beam will be less susceptible to wide-angle stray radiation and electronic counter measures.

It is still a further object of this invention to provide a survivable ground antenna system which is simple in construction, economical to produce and which utilizes conventional, currently available components that lend themselves to standard mass producing techniques.

For a better understanding of the present invention together with other and further objects thereof reference is now made to the following description taken in conjunction with the accompanying drawing and its scope will be pointed out in the appended'claims.

DESCRIPTION OF THE DRAWING FIG. 1 is a pictorial view of the survivable ground an tenna system of this invention located within the ground and showing a grounded conductive fence therearound;

FIG. 2 is a side elevational view shown partly in cross section of the survivable ground antenna system of this invention; and

FIG. 3 is an exploded pictorial view of the survivable ground antenna system of this invention showing in detail the various elements thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now made to FIG. 1 of the drawing which shows the survivable ground antenna system embedded within the earths surface 12 with only the domed weather cover 14 exposed to the elements. A clutter fence 16 surrounds the antenna system 10 and this fence 16 provides physical security against intruders, physiological protection against personnel irradiation and an inherent improvement in resistance to system degradation by electronic interference.

. FIGS. 2 and 3 show in detail the specific elements which make up the survivable ground antenna system 10 of this invention. These elements comprise a hemispheric reflector 18 made of any solid metallic material which is mounted in a rigid supporting cup 20 made of any suitable material such as concrete. A plurality of apertures 26 are located within both reflector l8 and supporting cup 20 in order to mount a point-source feed therein in a manner to be described hereinbelow. Supporting cup 20 is embedded within a hollow portion of the earth so as to only expose the domed weather cover 14 as shown in FIG. 1.

A point-source feed 22 is mounted on any suitable housing 23 having an electrical connector 24 attached thereto. The feed 22 protrudes through one of the apertures 26 located within the reflector 18 and supporting cup 20. This point-source feed 22 is roughly on a line including the target 27 which may be in a form of a satellite, and the center of generation of the sphere. For use with communications satellites 27 and a site location of approximately 40 latitude the apertures 26 would be located approximately 45 down into the hemisphere. It should be noted, however, that apertures 26 may take on a variety of locations. Since the satellites 27 are relatively stationary the point-source feed 22 may be mounted within any one of the apertures for approximate alignment with target 27. Furthermore, any precise alignment is accomplished by any suitable adjusting system such as a hydraulic subsystem 28 shown clearly in FIG. 2. This hydraulic subsystem 28 would allow for a precise adjustment of the feed 22 within the limits of the apertures 26.

The point-source feed 22 is directed toward the target 27 and is reflected to or from the spherical reflector 18 via a gregorian sub-reflector 30. Gregorian sub-reflector 30 is a small metallic reflector mounted beyond the locus of focal points of main reflector 18 and is supported by an ogive 32 which is rf-transparent. Opposite reflector 30 and at the rear of ogive 32 is a circular dished shaped section or plate 34 preferably made of metal which conforms to the spherical shape of the main reflector 18. The feed 22 is fixedly secured by any suitable securing arrangement to plate 34 by for example a grooved locking arrangement 36. Plate 34 serves to provide a continuous surface for reflector 18 covering aperture 26. The entire assembly of feed 22, ogive 32, plate 34 and sub-reflector 30 is positioned as a unit by hydraulic cylinders 28 for fine aiming of the point-source feed 22. Furthermore, the plate 34 including the other elements attached thereto may be locked in place by a vacuum seal produced by tube 38 operably connected to any suitable vacuum source (not shown) when the point-source" feed 22 has fixed upon the desired target 27. Hydraulic system 28 .could be computer controlled and run by the same electrical motors utilized on a conventional antenna.

At the base of main reflector 18 and supporting cup 20 is an opening 40 shown in FIG. 2 which leads to a cylindrical evacuation chamber 42 shown in FIG. 3. Chamber 42 provides an outlet for any debris which may have inadvertently collected within the spheric surface of reflector 18. The entire unit may be encased by a protective housing 44 which is also embedded within the ground.

A weather cover 14 of any suitable rf-transparent material such as fiberglass encloses the entire antenna assembly. Fence 16 surrounds the exterior of the antenna. This grounded fence 16 may be as much as 45 feet in height blocking Electromagnetic Radiation while not interferring with the satellite communication beam which would be at 45 elevation.

Although this invention has been described with reference to a particular embodiment, it will be understood to those skilled in the art that this invention is also capable of a variety of alternate embodiments within the spirit and scope of the appended claims.

I claim:

1. A survivable ground antenna system comprising a rigid supporting cup embedded within the ground, a main reflecting means mounted within said supporting cup, at least one aperture located within said main reflecting means and said supporting cup respectively, said aperture in said main reflecting means being aligned with said aperture in said supporting cup, means for communicating with a target adjustably mounted within said aligned pair of apertures and a means for protecting said communicating means secured to said reflecting means whereby said antenna system is capable of operation during adverse environmental conditions.

2. A survivable ground antenna system as defined in claim 1 wherein said main reflecting means is in the form of a hemispheric reflector.

3. A survivable ground antenna system as defined in claim 2 wherein said communicating means is fixedly secured to a plate moveably mounted within said hemispheric reflector 4. A survivable ground antenna system as defined in claim 3 further comprising an rf-transparent support secured at one end to said plate and a subreflector secured to the other end of said support opposite said communicating means.

5. A survivable ground antenna system as defined in claim 4 further comprising a means for locking said communicating means securely in place.

6. A survivable ground antenna system as defined in claim 5 wherein a hole is located at the bottom of said main reflector and said supporting cup providing an outlet for debris inadvertantlycollected in said main reflector.

7. A survivable ground antenna system as defined in claim 6 wherein said communicating means is in the form of a point-source feed.

8. A survivable ground antenna system as defined in claim 7 wherein said means for protecting said communicating means is an rf-transparent domed cover.

9. A survivable ground antenna system as defined in claim 8 wherein a hydraulic system adjustably mounts said communicating means.

10. A survivable ground antenna system as defined in claim 9 further comprising a grounded fencesurrounding said domed cover. 

1. A survivable ground antenna system comprising a rigid supporting cup embedded within the ground, a main reflecting means mounted within said supporting cup, at least one aperture located within said main reflecting means and said supporting cup rEspectively, said aperture in said main reflecting means being aligned with said aperture in said supporting cup, means for communicating with a target adjustably mounted within said aligned pair of apertures and a means for protecting said communicating means secured to said reflecting means whereby said antenna system is capable of operation during adverse environmental conditions.
 2. A survivable ground antenna system as defined in claim 1 wherein said main reflecting means is in the form of a hemispheric reflector.
 3. A survivable ground antenna system as defined in claim 2 wherein said communicating means is fixedly secured to a plate moveably mounted within said hemispheric reflector
 4. A survivable ground antenna system as defined in claim 3 further comprising an rf-transparent support secured at one end to said plate and a subreflector secured to the other end of said support opposite said communicating means.
 5. A survivable ground antenna system as defined in claim 4 further comprising a means for locking said communicating means securely in place.
 6. A survivable ground antenna system as defined in claim 5 wherein a hole is located at the bottom of said main reflector and said supporting cup providing an outlet for debris inadvertantly collected in said main reflector.
 7. A survivable ground antenna system as defined in claim 6 wherein said communicating means is in the form of a ''''point-source'''' feed.
 8. A survivable ground antenna system as defined in claim 7 wherein said means for protecting said communicating means is an rf-transparent domed cover.
 9. A survivable ground antenna system as defined in claim 8 wherein a hydraulic system adjustably mounts said communicating means.
 10. A survivable ground antenna system as defined in claim 9 further comprising a grounded fence surrounding said domed cover. 